New scientific evidence casts fresh doubt on the conviction of a nurse who was jailed for a minimum of 30 years for murdering four elderly women and attempting to kill another.

Glasgow-born Colin Norris was jailed for life in March 2008, when he was 32, after he was found guilty of murdering the women while working in Leeds General Infirmary and the city's St James's Hospital in 2002.

A doctor raised the alarm after noticing that one of the patients had suddenly and unexpectedly slipped into a hypoglycaemic coma from which she later died.

Norris has always protested his innocence and denied injecting patients with insulin. His case had been the focus of campaigners who fear a miscarriage of justice and is currently under review.